The truth is that the economy in D&D, if you put real thought into it, simply doesn't work. This means the DM has to house-rule any time something will have true economic impact that could cause the PCs to be out of whack on a wealth-to-level ratio basis. Not to say that the DM has to follow the wealth by level guidelines in the DMG, but whatever they are setting the CR in relation to, they have to monitor anything that impacts the economy that would throw that off.
I think this (and other writings within) is something to be considered in the process of creating your own shop and selling goods, as I am trying to do in another game. I don't think it requires being as hardcore, but it's something to consider alright. Hmmm...In the Upkeep variant rules of the DMG, it says that one of the Upkeep levels is about the daily wage of a commoner. Also, this has some basics. Dungeonomicon (3.5e Sourcebook)/Economicon - Dungeons and Dragons Wiki

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.